1. Field of the Invention
The present invention relates to a construction of coupling spline sections of an automatic transmission.
2. Description of the Related Art
An automatic transmission constituting three axles has a mission case including an input shaft, a counter shaft, a drive shaft which are arranged in parallel. On the above shafts, there are arranged various elements such as a transmission unit, a gear and the like.
As is seen in FIG. 5, there is provided a counter driven gear 302 which is coaxially coupled with a counter shaft 300, wherein the counter shaft 300 is disposed between an input shaft and a dive shaft while the counter driven gear 302 meshes with a counter drive gear 301 disposed on the input shaft's side.
The counter shaft 300 has a first end side (left in FIG. 5) which is formed with a small-diameter shaft section 304, and a second end side (right in FIG. 5) which is formed with a reduction gear 306 united with the small-diameter shaft section 304.
The small-diameter shaft section 304 has an outer periphery which is formed with a spline section 308. There is formed a tubular section 310 which is united with the counter driven gear 302. The tubular section 310 has an inner periphery which is formed with a spline section 312. The spline section 312 of the tubular section 310 can be coupled with the spline section 308 of the small-diameter shaft section 304. Moreover, a nut 314 is screwed down on a first end (left in FIG. 5) of the small-diameter shaft section 304, in such a manner as to press the tubular section 310 on the reduction gear 306's side. This can constrain an axial movement of the counter driven gear 302.
There is provided a radial bearing 318 between an outer periphery of the tubular section 310, and the mission case 316. The counter shaft 300 can be rotatably born by means of the radial bearing 318.
The spline section 308 of the small-diameter shaft section 304 can be coupled, in an entire axial range thereof, with the spline section 312 of the tubular section 310 in a press fitting state.
Thus, too great a press fitting force may expand the tubular section 310, thereby applying a stress to the radial bearing 318 from inside. Too great a stress may reduce accuracy of the radial bearing 318 in rotatably bearing the counter shaft 300, to thereby deteriorate durability.
For preventing possible failures such as split, crack and the like (which may be caused by the stress applied to the inner periphery of the tubular section 310), the tubular section 310 is to be designed thick. This may involve a large size of the whole unit.